Aristotle's Theory of Tragedy in the Poetics

Tragedy- an imitation of an action that is serious, complete, and of certain magnitude that includes arousing pity and fear. There are six parts to a tragedy: Plot, Characters, Diction, Thought, Spectacle, and Melody.
Simple Plot- have only a change in fortune (catastrophe).
Complex Plot-(Preferred by Aristotle) have reversal of intention (peripeteia) and recognition (anagnorisis) with the catastrophe.
Hamartia- tragic mistake
Katharsis- purging. Aristotle uses the term in a medical way, referring to purging of the emotions pity and fear.
Deus ex machine- an unsolvable problem is suddenly solved by an unexpected intervention.